Vulcanization of rubber



Patented Aug. 7, 1945 UNITED, z STATES OFF- C I z vULcANIzA'rIoN'or RUBBER 5 e George E. P. Smith, Jr., Akrb omo, assignor'to.

' The Firestone Tire & Rubber Company, Akron,

Ohio, a corporation of Ohio L z .No l )rawing. Application April 10,1944, W '7 7 Serial No. 530,391

6 Claims. v (01. 260 185} j This invention relates to the art of vulcanizing rubber, and relates more particularly to the acceleration of the vulcanization of a rubber.

Y The objects of the invention include a' new methodof vulcanizing a rubber, a rubber com- 5 J position capable of vulcanizing rapidly .on the application of heat thereto, and a vulcanized rubber product having, desirable properties. Other objects will be manifest in the description of the invention which follows.

As a part of the present invention it has been "d ve ed ha Part l .r u ed;2r.mema i m thi zv aisia emcee a ele tor h vulcanization of a rubber. The accelerators are not was tested as arubber vulcanization accelerator in the following rubber formula;

' 'Ingred nts 33; 2

.Rubbcr (smoked sheets). 100. 'Sulfur; 3. Stearic acid l 1. Zinc oxide 5. 2-mercapto-tetrahydrobenzotlnazole 0.

The above rubber-composition was mixed in a a conventional manner and then heated for 40,

Z-mercapto-tet ahydrobenzothiazoles of the fol-2231 lowing general formula:

wherein R. is hydrogen, an alkyl or alkoxy radical. The accelerators may, -for example, be prepared by reacting an alpha chloro cyclohexanone with ammonium dithiocarbamate. Examples of thiazoles useful as' accelerators are 2-mercaptotetrahydrobenzothiazole, 2-mercapto-5-methyltetrahydrobenzothiazole, zmercapto 5 ethyl-H tetrahydrobenzothiazole, 2 mercapto 5,6 dimethyl-tetrahydrobenzotl'liazole, 2mercapto-4 ethyl tetrahydro benzothiazole, 2 mercapto 4- methyl tetrahydrobenzothiazole, 2 mercapto- 5,6-diethyl-tetrahydrobenzothiazole, 2-mercapto-4,5-diethyl tetrahydrobenzothiazole, 2 mercapto 5 methyl fi-methoxy tetrahydrobenzothiazole, 2- mercapto-7-ethyl-tetrahydrobenzothiazole, and 2-mercapto-5-methoxy-tetrahytallizing the product from benzene a white solid was obtained meltingat 174-176 C. The prodand minutes .at 280j F. The following physical testing datawere obtained on the heated composition:

Tensile strengglailixl 1bs./in at z z 600% Minutes A rubber composition corresponding to the above formula but containing no organic vulcanizationaccelerator does not cure on, heating at 280 F. for the shorter periods of time. On heating such compositions for 60 or 100 minutes at this temperature the composition, becomes slightly vulcanized, but is very much undercured, attaining tensile strengths of less than 1000 pounds per square inch. Hence, it is seen that y the new class of accelerators is remarkably efficient in producing a fast curing rubber composition, which, uponbeing heated, changes into a rubber vulcanizate having high tensile strengths and other desirable properties, such as good resistance to deterioration on aging in the presence of heat or sunlight.

The new class of accelerators is equally effective in rubber tread compounds, latex compounds or other conventional types of vulcanizable compounds of rubber, reclaimed rubber or synthetic rubber. The various synthetic rubbers vulcanizable by heating with sulfur are herein considered equivalent to natural rubber, examples being butadiene polymers, isoprene polymers and various interpolymers of conjugated diolefins and vinyl compounds, such as Buna S (copolymer of butadiene and styrene) and Buna N (copolymer of butadiene and. acrylonitrile). Although sulfur has hereinabove been mentioned as the preferred vulcanizing agent, other known vulcanizing agents susceptible to acceleration are contemplated.

Accelerator activators, especially of the basic type, may be employed with the new class of accelerators when extremely rapid vulcanization is desired, especially at low temperatures. The new accelerators may be emp oyed in other pr p tions than the proportion shown in the above example, but will normally be utilized in the range of 0.1 to 10 parts per 100 parts of rubber.

Modification may be resorted to and obvious chemical equivalents substituted in the specific examples of the invention without departing from the spirit or the scope of the invention as defined in the appended claims.

What is claimed is:

1. The method of vulcanizing rubber which includes heating a rubber and sulfur in the presence of 2-mercapt0-tetrahydrobenzothiazole.

2. A vulcanizable rubber composition including sulfur and 2-mercapto-tetrahydrobenzothiazole.

3. A vulcanized rubber product prepared by heating a rubber and sulfur in the presence of 2-mercapto-tetrahydrobenzothiazole.

4. The method of vulcanizing rubber which includes heating a rubber and sulfur in the presence of a Z-mercapto-tetrahydrobenzthiazole of the formula wherein R is a member of the group consisting of hydrogen, alkyl radicals and alkoxy radicals.

5. A vulcanizable rubber composition including sulfur and a 2-mercapto-tetrahydrobenzothiazole of the formula i CH R o \C-N o-sn R-CH o-s/ o I R wherein R is a member of the group consisting of hydrogen, alkyl radicals and alkoxy radicals.

6-. A vulcanized rubber product prepared by heating a rubber and sulfur in the presence of a 2 -mercaptotetrahydrobenzothiazole of the formula *1 f5 R'CH C-N H HH 'ROH -s \OH 1'2 wherein R is a member of the group consisting of hydrogen, alkyl radicals and alkoxy radicals.

GEORGE E. P. SMITH, JR. 

